Current Status and Trends
Neodymium magnets are graded according to their maximum energy product, which relates to the magnetic flux output per unit volume. Higher values indicate stronger magnets. For sintered NdFeB magnets, there is a widely recognized international classification. Their values range from 28 up to 52. The first letter N before the values is short for neodymium, meaning sintered NdFeB magnets. Letters following the values indicate intrinsic coercivity and maximum operating temperatures (positively correlated with the Curie temperature), which range from default (up to 80 °C or 176 °F) to AH (230 °C or 446 °F).
Some important properties used to compare permanent magnets are:
Remanence (Br), which measures the strength of the magnetic field.
Coercivity (Hcj), the material’s resistance to becoming demagnetized.
Maximum energy (BHmax), the density of magnetic energy, characterized by the maximum value of magnetic flux density(B) times magnetic field strength (H).
Curie temperature (TC), the temperature at which the material loses its magnetism.
Neodymium has a negative coefficient, meaning the coercivity along with the magnetic energy density (BHmax) decreases with temperature. Neodymium-iron-boron magnets have high coercivity at room temperature, but as the temperature rises above 100 °C (212 °F), the coercivity decreases drastically until the Curie temperature (around 320 °C or 608 °F). This fall in coercivity limits the efficiency of the magnet under high-temperature conditions such as in wind turbines, hybrid motors, etc. Dysprosium (Dy) or terbium (Tb) is added to curb the fall in performance from temperature changes, making the magnet even more expensive.
Neodymium material is brittle and prone to chipping and cracking, so it does not machine well by conventional methods. Machining the magnets will generate heat, which if not carefully controlled, can demagnetize the magnet. Many shapes that would be easy to manufacture in a steel or aluminum part are not necessarily feasible in a neodymium magnet. Complex shapes or shapes with thin cross sections might not be possible. The neodymium magnet shape should fit within the boundaries of a 220 x 220 x 80mm box, with the magnetization direction in the 80mm direction.
Magnets can be supplied in the magnetized or non-magnetized state. For the delivery of magnetized parts we have various packaging methods available.
Neodymium magnets have replaced alnico and ferrite magnets in many of the myriad applications in modern technology where strong permanent magnets are required, because their greater strength allows the use of smaller, lighter magnets for a given application.